Process of producing a magnetic read head having a multilayer magnetoresistant element and a concentrator

ABSTRACT

A process of producing a magnetic read head which includes a multilayer magnetoresistant element and a concentrator. The magnetic read head is produced to include a multilayer magnetoresistant element across a head gap of the concentrator positioned to a rear of pole pieces defining the gap of the head. Such a magnetic head may find particular application in magnetic recording systems.

This is a division of application Ser. No. 08/330,674 filed on Oct. 28,1994, now abandoned.

DESCRIPTION

1. Technical Field

The present invention relates to a magnetic read head having amultilayer magnetoresistant element and a concentrator, as well as toits production process. It is used in magnetic information recording.

2. Prior Art

Magnetic read heads with a magnetoresistant element are known. For someof them the magnetoresistant element is placed beneath the head gap andthis is e.g. described in FR-A-2 645 314 and FR-A-2 657 189. In others,the magnetoresistant element is placed to the rear of the magneticcircuit and is used for closing the latter, as is e.g. described inEP-A-472 187 and EP-A-475 397.

The heads using a magnetoresistant element closing the magnetic circuitto the rear of the head operate with monolithic magnetic materials. Theyare mainly compounds based on iron and nickel, or compounds based oniron, nickel and cobalt. However, with such materials if themagnetoresistant element is used in the longitudinal position, thesensitivity is low, because the magnetic reading field is parallel tothe detection current flowing in the element. This sensitivity can beimproved by making the element operate transversely, i.e. by turning itby 90° so that the magnetic reading field traverses the element in itswidth direction, the detection current still being applied in the lengthdirection. However, this arrangement leads to construction problems.

The present invention aims at obviating these disadvantages.

3. Description of the Invention

To this end, the invention firstly recommends the use, for the formationof the magnetoresistant element, of a multilayer instead of monolithicmaterial. It is a question of materials constituted by a stack ofmagnetic layers separated by non-magnetic metal layers.

The multilayer magnetic structures use cobalt, iron, copper, chromium,nickel, iron and nickel alloys, silver, gold, molybdenum, ruthenium andmanganese are described in the article by H. YAMAMOTO and T. SHINJO,published in "IEEE Translation Journal on Magnetics in Japan", vol.7,no.9, September 1992 with the title "Magnetoresistance of Multilayers",pp.674--684.

Multilayer materials have interesting properties such as a considerablemagnetoresistive effect, low saturation field, low coercivity and goodannealing behavior. The best structures obtained up to now have beenformed by FeNi layers separated by copper layers, as described in thearticle by S. S. P. PARKIN entitled "Oscillations in GiantMagnetoresistance and Antiferromagnetic Coupling in [Ni₈₁ Fe₁₉ /Cu]_(N)N Multilayers", published in "Appl. Phys. Lett." 60, no.4, January 1992,pp.512-514 and the article by R. NAKATANI et al published in "IEEETransactions on Magnetics", vol.28, no.5, September 1992, pp.2668-2670and entitled "Giant Magnetoresistance in Ni-Fe/Cu Multilayers Formed byIon Beam Sputtering".

Good results are also obtained with structures formed from FeNi filmsseparated by silver coatings, as described in the article by B. RODMACQet al published in "Journal of Magnetism and Magnetic Materials", 118,1993, pp.L11-L16 and entitled "Magnetoresistive Properties and ThermalStability of Ni-Fe/Ag Multilayers".

These new materials have the property of being highly magnetoresistive,i.e. have a relative resistivity variation ratio from 10 to 20% and lowsaturation magnetic fields below 40 kA/m.

With materials of the multilayer type, there is a high sensitivity tothe flux or flow when the magnetic field is applied in the longitudinaldirection. For a constant magnetoresistance coefficient, the sensitivityis at a maximum when the saturation field is weak. The saturation fieldcorresponds to the magnetic field which it is necessary to apply inorder to orient, in the same direction and the same sense, themagnetization of each of the different magnetic layers.

In a field parallel to the length of a bar of a multilayer material,said field is equal to the coupling field of the unitary layers. In thetransverse field, the appearance of demagnetizing fields increases thesaturation field, which reduces sensitivity.

In other words, it is preferable from the sensitivity standpoint, toplace the magnetoresistant element in a longitudinal position, i.e. withits largest dimension parallel to the magnetic field to be read.

Besides this first feature of the invention, linked with the use ofmultilayer materials in the longitudinal position, the inventionrecommends a second feature, which is that of using a magnetic fieldconcentrator formed from two magnetic layers defining a second head gapacross which there is the magnetoresistant element. In this way, thereis a concentration of the magnetic reading field in the magnetoresistantelement, which increases the measuring signal.

More specifically, the present invention relates to a magnetic readinghead comprising a magnetic circuit having two pole pieces separated by afirst head gap and a longitudinal magnetoresistant element, said headbeing characterized in that it also comprises two magnetic layers incontact with the pole pieces and spaced from one another by a secondhead gap located beneath the first, said magnetic layers having a widthwhich decreases on approaching the second head gap and thus forming amagnetic field concentrator, the longitudinal magnetoresistant elementbeing placed across said second head gap and being made from amultilayer material constituted by a stack of magnetic layers separatedby non-magnetic metal layers.

In an advantageous embodiment, the magnetoresistant element is formedfrom several parallel longitudinal portions arranged juxtaposed acrossthe second head gap, said portions being electrically connected inseries by their ends by transverse portions.

The read head can also comprise an electrical conductor able tolongitudinally polarize the magnetoresistant element.

The read head according to the invention can easily be completed bymeans able to permit its operation in writing. These means consist of alower pole piece and a conductor coil.

The present invention also relates to a process for the production ofthe head as defined hereinbefore.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a subassembly relative to writing means.

FIG. 2 shows in section the construction of a concentrator.

FIG. 3 shows the concentrator in plan view.

FIG. 4 illustrates an intermediate stage of depositing an insulatinglayer.

FIG. 5 shows in plan view connection elements.

FIG. 6 shows in section a magnetoresistant element.

FIG. 7 shows a magnetoresistant element in plan view.

FIG. 8 illustrates an intermediate stage of depositing a new insulatinglayer.

FIG. 9 shows the formation of openings in the insulating layer.

FIG. 10 shows the conductor elements and a conductive polarizingelement.

FIG. 11 shows the read-write head finally obtained.

DETAILED DESCRIPTION OF AN EMBODIMENT

The features of the read head according to the invention will becomeapparent through the successive stages of its production process.

If it is only wished to obtain a read head, use will initially be madeof a substrate, e.g. constituted by a silicon wafer. If it is wished toobtain a read head also able to operate in the writing mode, thesubassembly as illustrated in FIG. 1 will initially be used.

This subassembly is obtained by operations known to the expert and whichare e.g. described in FR-A-2 645 314 (or its corresponding U.S. Pat. No.A-5 208 716) and will not be described in detail here. It is merelynecessary to point out that on an e.g. silicon semiconductor substrate10 is formed a recess 12, in which is deposited a lower magnetic layer14 and two magnetic pillars (16₁, 16₂).

A conductor coil 18 is then wound around the pillars 16₁, 16₂, wherebysaid coil-can be made from copper. Only a few turns are illustrated inFIG. 1, but it is clear that in practice there can e.g. be 16 turns inthe same plane, distributed in the form of twice 8 turns. This coil willbe buried in an insulating layer 20.

The operations necessary for producing the reading part then commencefrom the subassembly of FIG. 1 taken as the substrate. Firstlydeposition takes place of a magnetic material layer and the latter isetched in order to form the two pieces 301, 302, which are spaced fromone another by a head gap 32 (FIGS. 2 and 3). The width of these layersdecreases on approaching the head gap 32.

FIG. 3 shows layers 30₁, 30₂, which have a trapezoidal shape, but anyother shape is possible provided that the magnetic flux concentrationfunction is fulfilled. The material used for producing said concentratorcan be iron nickel. On the assembly is then deposited a first, e.g.silica insulating layer 34 with a thickness of 0.1 to 0.5 μm (FIG. 4).

This is followed by the deposition of a conductive material layer, whichis preferably of a refractory material such as titanium, tungsten ormolybdenum. The thickness of this layer can be between 0.05 and 0.5 μm.On said metal layer photolithography is then performed, so as to formthe external elements 21, 23, 25, 27, the internal elements 41, 43, 45,47 and conductive strips 31, 33, 35, 37 linking the internal elementswith the external elements (FIG. 5).

This is followed by the production of the magnetoresistant element. Forthis purpose, a multilayer magnetoresistant material layer is depositedand is etched in order to form a magnetoresistant element 50 (FIG. 6).The multilayer magnetoresistant material can e.g. be Ag/FeNi.

In the embodiment illustrated in FIG. 7, the magnetoresistant element 50has parallel longitudinal portions (a, b, c, d, e) arranged in ajuxtaposed manner across the head gap 32 and transverse portions (A, B,C, D) linking the ends of the longitudinal portions. Themagnetoresistant element is connected to the elements 41 and 47.

The longitudinal portions project from each side of the head gap 32 andoverlap the two pieces of the concentrator by approximately 2 μm. Forexample, if the head gap 32 has a length of 4 μm, the length of thelongitudinal strips will be approximately 8 μm.

On the assembly is then deposited a further insulating layer 52, e.g. ofsilica (FIB. 8). By photolithography, two openings 63, 65 are formed inorder to free the elements 43, 45, which will be used for connecting thepolarization conductor. In this operation, it is also possible to freethe ends A, B, C and D of the magnetoresistant element through openings54, 55, 56, 57 (FIG. 9).

This is followed by the deposition of a further metal layer, e.g. of thesame type as the previous one and with a relatively limited thickness ofe.g. 0.5 μm, followed by a conductive layer, e.g. of copper. Byphotolithography, two elements 73, 75 are left in the openings 63, 65,which have been freed and between said two ends is produced a ribbon 80,which will serve as the polarization conductor. Simultaneously, theelements 81, 82, 83, 84 are left in the openings 54, 55, 56, 57 made atthe ends of the magnetoresistant element. These elements short-circuitthe transverse arms A, B, C, D of the magnetoresistant element. In thisway, only the longitudinal arms a, b, c, d and e are active.

The production of the head is completed (FIG. 11) by producing two polepieces 90₁, 90₂ separated by a head gap 100, everything being embeddedin an insulant 102.

The connection elements of the magnetoresistant element and thepolarization conductor are displaced towards the periphery of the device21, 23, 25, 27, so that there is no problem in establishingintraconnections across the insulating layer 102.

In the embodiments described hereinbefore, the magnetoresistant element50 is placed above the second head gap 32. It would obviously not passoutside the scope of the invention to position it below the same. In thesame way, the polarization conductor 80 could be located below insteadof on the magnetoresistant element.

What is claimed is:
 1. A process for producing a magnetic read head,comprising the steps of:depositing on a substrate a magnetic materiallayer; etching said deposited magnetic material layer in order to formtwo magnetic layers spaced from one another by a first head gap, saidtwo magnetic layers having a width decreasing on approaching the firsthead gap; depositing a first insulating layer on the substrate and firsthead gap; depositing a metal layer on the first insulating layer andetching the metal layer in order to form first, second, third and fourthinternal conductor elements connected by four respective conductivestrips to four respective external elements; depositing on said metallayer a multilayer magnetoresistant material layer; etching saidmagnetoresistant material layer to form a magnetoresistant element, saidmagnetoresistant element having two ends in contact with the first andsecond of the four internal conductor elements; depositing a secondinsulating layer on said multilayer magnetoresistant material layer;etching said second insulating layer in order to free the third andfourth internal conductor elements; depositing a conductive layer on thesecond insulating layer and etching the conductive layer to leave aribbon having two ends in contact with the third and fourth internalconductor elements, said ribbon extending across the magnetoresistantelement; and forming two pole pieces bearing on the two magnetic layers,said two pole pieces being separated by a second head gap.
 2. Theprocess according to claim 1, wherein the step of etching themagnetoresistant material layer etches said magnetoresistant element inthe form of parallel, longitudinal portions, arranged in a juxtaposedmanner across the first head gap separating the two magnetic layers andtransverse portions connecting the ends of the longitudinal portions. 3.The process according to claim 2, wherein in the step of etching thesecond insulating layer, not only are the third and fourth internalconductor elements etched and freed, but the second insulating layer isetched to further also free the transverse portions of themagnetoresistant element, so that in the step of depositing theconductive layer, formation takes place of transverse conductors on thetransverse portions of the magnetoresistant element.
 4. The processaccording to claim 1, wherein before the step of depositing saidmagnetic material layer on said substrate, further comprising the stepof:forming a subassembly of the substrate, on which is formed a polepiece with two pillars and a conductor coil embedded in an insulant.